An important factor for the correct operation of most refrigeration compressors is the adequate lubrication of the components thereof which have a relative movement therebetween. The lubrication is obtained by pumping the lubricant oil provided in an oil reservoir defined in the interior of a generally hermetic shell of said compressors, in a lower portion of said shell. The oil is pumped until reaching the parts with relative movement of the compressor, wherefrom said oil returns, for example, by gravity, to the oil reservoir.
In some known constructions, the compressor comprises a generally vertical crankshaft carrying a lubricant oil pump, which conducts said oil to the compressor parts to be lubricated, using the rotation of said crankshaft. In these constructions, the oil is pumped from the oil reservoir by centrifugation and mechanical dragging.
In these constructions, the crankshaft presents a portion of its extension provided, externally (WO2005/047699) or internally (WO96/29516), with helical grooves which conduct the lubricant oil from the oil reservoir to the relatively moving parts of the compressor provided away from the oil reservoir.
In WO2005/047699, a tubular sleeve is provided around part of the crankshaft which presents the helical grooves, said tubular sleeve being attached to the compressor shell or to the stator.
WO96/29516 presents a solution in which the crankshaft has part of its extension defining a conduct inside which is mounted, with a radial gap, a pump body, said solution presenting one of the parts of inner wall of the tubular shaft and outer wall of the pump body provided with helical grooves.
There are known some prior art solutions for oil pumping in variable speed compressors. In these constructions (WO93/22557, U.S. Pat. No. 6,450,785, JP2005-337158), the crankshaft inferiorly carries a pump body provided with surface channels and internally disposed in a tubular sleeve, one of the parts defined by the pump body and the tubular sleeve being rotatively stationary in relation to the other part, so as to provide the dragging effect on the oil being drawn by centrifugal force, resulting from the rotation of the motor.
Solution WO93/22557 presents the pump body externally provided with helical grooves and affixed to the crankshaft so as to rotate therewith, the tubular sleeve being attached to the electric motor stator by a fixation rod, said tubular sleeve being mounted around the pump body with a radial gap.
Such solution allows friction wear to occur between the parts of pump body and tubular sleeve, as well as mechanical losses, as a result of the rigid fixation between said tubular sleeve and the stator and of practically inevitable misalignments between the pump body and the tubular sleeve.
Documents U.S. Pat. No. 6,450,785 and JP2005-337158 each presents a solution in which the pump body provided with helical grooves in its outer surface is inferiorly affixed to the electric motor stator through a fixation rod with a U-shaped profile, and the tubular sleeve is affixed to the crankshaft of the compressor so as to rotate therewith. Each of these solutions present a construction in which the fixation rod is rigidly affixed to the electric motor stator (or to a motor protector inferiorly affixed in said stator), allowing only a certain angular movement of the pump body around axes contained in the lower fixation plane of the pump body to the fixation rod, said plane being orthogonal to the crankshaft of the compressor. Thus, the fixation rod can be elastically deformed to allow the pump body to incline so as to accommodate itself in the interior of the tubular sleeve. However, as the pump body is not free to be displaced, in its entirety, in directions orthogonal to the crankshaft, as a function of the rigid fixation of the fixation rod to the motor, it is not capable of compensating for construction or mounting misalignments, in order to occupy a position in which its axis is concentric or parallel to the axis of the tubular sleeve.
Although reducing wear and friction losses, these known prior art solutions still lead to a certain efficiency loss, particularly considering the inevitable dimensional deviations during manufacture and assembly.
The Brazilian co-pending patent document PI0604908-7 (WO2008/052297) presents the pump body freely displaceable in the interior of the tubular sleeve, in radial directions orthogonal to the crankshaft and rotatively locked in relation to the rotor, the supporting means of said pump body being a rigid rod having the first portion loosely fitted in a radial housing provided in the lower end portion of the pump body, so as to support the latter. Thus, the dimensional deviations of both the pump body and the tubular sleeve are absorbed by said pump body freely moving through the gap between the lower radial housing of the pump body and the rigid rod.
While said prior art solution PI0604908-7 minimizes the effects of the dimensional deviations regarding wear and friction losses, it introduces the collateral effect of providing intermittent contacts between the components defined by the pump body and supporting rod. The contact between the surfaces, upon high rotation speeds of the mechanism, generates an undesirable noise in the operation of the compressor.
Besides the issues regarding the free displacement of the pump body inside the tubular sleeve, in radial directions orthogonal to the crankshaft, with a rotative locking in relation to the pump rotor, the prior art solutions for the oil pump of a refrigeration compressor present a deficient fixation of the pump part (pump body or tubular sleeve) to the crankshaft or rotor, when said pump part is made of a non-metallic material. In the known solutions having a tubular sleeve or a pump body (EP0728946) in a material different from that of the crankshaft or rotor, particularly a non-metallic material, such as plastic, there occurs with time a degradation in the quality of the fixation obtained, since the operational conditions of the compressor, such as heating, affect the degree of interference between the parts affixed to each other. In case the tubular sleeve or the pump body is made of plastic, this material will present deformation when submitted to heating upon operation of the compressor, causing loss of said interference and consequent loosening of the fixation initially obtained.